Combustion chamber with primary and secondary air flows



March 26, 1963 H. HERING ETAL COMBUSTION CHAMBER WITH PRIMARY AND SECONDARY AIR FLOWS Filed Oct. 2, 1956 INVE m'mas HANS Hsama Lemma Msuz EDOUARD CAFFIER ilil ATTORNEYS United States Patent It is difficult to design combustion chambers which are able to comply at the same time with the conditions which enable both a high eificiency (total combustion), a very low limit of extinction, a low loss of pressure and especially a uniform distribution of temperature in the radial and peripheral directions to be obtained. In gasturbine engines, it is in fact desirable to prevent local peaks of temperature produced by the combustion, since such peaks are dangerous for the blades of the turbine.

The distribution of temperatures gives rise to great difiiculties when the mixture becomes increasingly rich, and thus the increases in power of turbo-machines are limited by thermal considerations.

The present invention has for its object a combustion chamber device which complies to a very great extent with the requirements of efiiciency, low limit of extinction, small pressure losses and good distribution of temperatures.

In this device, the combustion chamber proper or flametube comprises a reduced section in an intermediate portion on the downstream side of the points of admission of primary air and of fuel.

The applicants have found that with a reduction in section which is sufficiently pronounced, it is possible not only to obtain combustion of the fuel in the primary air on the upstream side of this reduced portion, but also and especially to make the temperature uniform by contraction of the flow as it passes through the reduced portion, thus preventing the excessive temperature which may exist in certain of the streams of the jet, this last result being of course of great value in the supply of gas turbines.

The reduction in section of the combustion chamber may be obtained by means of projections formed over all or part of the periphery of the said chamber.

Orifices for the supply of secondary air are provided in the combustion chamber on the downstream side of the reduced portion and on the upstream side of the admission to the turbine. A suitable arrangement of these orifices enables the secondary air to be mixed with the gases produced by the primary combustion so as to obtain a mixing eflect which further contributes to the uniformity of temperatures.

In the accompanying drawings:

FIGURE 1 is a diagrammatic longitudinal section of an arrangement embodying the invention;

FIGURE 2 is a similar view of a modified form:

FIG. 1 shows a combustion chamber which may in the first place be assumed to be tubular for the sake of clearness of explanation, that is to say it comprises a mean axis A-A located inside this chamber. The air supplied from the compressor arrives through the conduit 1 ice and divides into two parts, one part forming the primary air of combustion passing in the direction of the arrows f into the combustion chamber proper or flame-tube 2, through one or a number of orifices formed in the head of this tube, the other part of the air circulating inside the space formed between the flame-tube 2 and the flared conduit 1a and passing into the said flame-tube towards its end portion. The example given in the drawing shows an admission device for primary air of known type, comprising two concentric open tubes 3, 4 of frusto-conical shape, connected to each other by radial arms 5. The fuel injector 6 discharges in the axis of the internal tube 3. A part of the primary air which passes in through the large orifice 7 formed at the head of the tube 2, passes through the annular space between the internal tube 3' and the injector 6. The greater part of the primary air passes into the channels formed all around the tube 3 by this tube itself, the radial arms -5 and the peripheraleral tube 4. The radial arms form wake zones on the downstream side of the flow, in which the flame may be initiated and stabilized.

Other burner devices exist which also comprise stabilizing screens playing the same part as the radial arms 5, in order to create wake zones in which the flame may be stabilized. Whatever may be the nature of the device, measurements made in the same rectangular cross-section of the tube 2 show the existence of zones in which the temperature is excessive and which coincide with the wake of the screens.

In order to make the temperature uniform, the form of embodiment of the invention shown in FIG. 1 comprises a narrowed portion 8 of the tube 2 at a certain distance on the downstream side of the origin of this tube, followed by a sharp flared portion 9 of the wall of the tube. The narrowed section 8 imposes a contraction on the jet of gas in course of ignition. The streams of burnt gases at high temperature and the less hot streams of air are thus displaced transversely by the efiect of the contraction, brought into intimate contact and mixed together, which eliminates the local peaks of temperature. The abrupt flaring 9 of the wall following the narrowed portion 8, produces an expansion of the jet with a reduction in its speed, but as the divergence is greater than that of the divergent portion of a correct diffuser, the jet leaves the wall 9 and produces vortices, which is also favorable to uniformity of temperature. In addition, the passage of the jet through the narrowed portion 8 produces a loss of pressure which facilitates the intake of secondary air through the orifices such as 10 formed on the downstream side of the said narrowed portion. Finally, the gases which are admitted to the distributor d of the turbine, have a better distribution of temperature than is the case with present devices.

The distance which separates the reduced portion 8 from the head portion of the flame-tube, and also the amount of this reduction (ratio of cross-sections) may be determine d by experiment in each particular case.

The reciprocal adaptation of the shape of the combustion chamber, of the number, the shape, the dimensions and the arrangement of the admission openings for secondary air to the value of the narrowed section and to its position enables the distribution of temperatures to be controlled as desired.

By way of example, FIG. 1 shows a narrowed portion, the distance of which from the origin of the tube 2 is a little greater than half the length of this tube between its intake and its outlet towards the distributor d of the turbine, while the diameter of the narrowed sections is ap proximately half the diameter of the tube on the upstream side of the narrowed portion.

The form of embodiment given in FIG. 2 differs from that described above by the presence of two successive narrowed portions 8 and 8a, which play their part in succession in creating uniform temperature condition.

The forms of embodiment'described are of course applicable to the case of annular chambers, the tubes 1, 1a and 2 then having an annular shape generated by rotation of the profiles shown on the drawing about an axis parallel to A-A but displaced (in general the common axis of the compressor and the turbine), and the burners such as 3 and 4 being distributed around this axis.

What we claim is:

1. A combustion chamber comprising a flame-tube ex tending therein in a fore-and-aft direction and bounding an inner space separated from a surrounding outer space of said chamber, saidjflame-tube having, in an intermedi ate zone thereof, a sudden constriction smoothly connected with a divergent downstream section, the portion of said inner space upstream of said constriction being gastightly separated from the surrounding outer space 4. whereas the portion of said inner space downstream of said constriction communicates with said outer space through ports formed in the divergent section of the flame-tube.

2. Combustion chamber as claimed in claim 1, wherein the ratio of the width of the constriction, measured transversely of the general flow direction to the maximum width of the upstream portion of said inner space similarly measured, is of the order of 0.5.

References Cited in the file of this patent UNITED STATES PATENTS 945,967 Mahr Jan. 11, 1910 2,525,206 Clarke Oct. 10, 1950 2,546,432 Darling Mar. 27, 1951 2,644,512 Durr July 7, 1953 2,687,010 Ellis Aug. 24, 1954 2,699,648 Berkey Jan. 18, 1955 2,825,202 Bertin et a1 Mar. 4, 1958 2,828,609 Ogilvie Apr. 1, 1958 2,907,171 Lysholm Oct. 6, 1959 FOREIGN PATENTS 962,581 France Dec. 12, 1949 998,079 France Sept. 19, 1951 687,667 Great Britain Feb. 18, 1953 726,491 Great Britain Mar. 16, 1955 

1. A COMBUSTION CHAMBER COMPRISING A FLAME-TUBE EXTENDING THEREIN IN A FORE-AND-AFT DIRECTION AND BOUNDING AN INNER SPACE SEPARATED FROM A SURROUNDING OUTER SPACE OF SAID CHAMBER, SAID FLAME-TUBE HAVING, IN AN INTERMEDIATE ZONE THEREOF, A SUDDEN CONSTRICTION SMOOTHLY CONNECTED WITH A DIVERGENT DOWNSTREAM SECTION, THE PORTION OF SAID INNER SPACE UPSTREAM OF SAID CONSTRICTION BEING GASTIGHTLY SEPARATED FROM THE SURROUNDING OUTER SPACE WHEREAS THE PORTION OF SAID INNER SPACE DOWNSTREAM OF SAID CONSTRICTION COMMUNICATES WITH SAID OUTER SPACE THROUGH PORTS FORMED IN THE DIVERGENT SECTION OF THE FLAME-TUBE. 